The present invention relates to an apparatus for transferring and weighing materials and, more particularly, to an apparatus for automatically transferring and weighing small quantities of powder materials.
One of the most fundamental routines for a chemist is preparation of samples from dry powdered materials. Often times, the chemist is required to measure very small quantities of one or more powders, e.g., on the order of 1-100 mg to form the sample.
Conventional powder dispensing stations are designed around the assumption that a relatively large amount of powder is available for dispensing. Conventional systems for weighing of powders include screw, rotary, vibratory, roll, shaker and revolving plate feeders. More specifically, all of these devices are designed for a large quantity of bulk powder to be continually dispensed into feed lines or vials. Therefore, these devices are not designed to be used in applications where a small quantity of powder is to be weighed. In a similar manner, these devices are not capable of being used when the powder material is contained within a small vial as is the case many times when a chemist or the like needs to weigh a small quantity of powder material.
Conventional powder dispensing and weighing systems also have other associated disadvantages. For example, one of the more common apparatuses for weighing a powder material includes a vibrating feeder provided at an outlet of a hopper for automatically feeding the powder material into a weighing container, e.g., cup or vial, mounted on an electronic weighing device. This type of device is only designed for weighing one kind of powder material. Accordingly, in the case of weighing other kinds of powder materials, it is necessary that the powder hopper is interchanged with other powder hoppers and the vibrating feeder is also interchanged or washed so as not to be mixed or contaminated by the powder material which has been previously weighed. This type of operation requires considerable time and is also costly due to the process being labor intensive.
Furthermore, there are other problems that make it difficult to perfectly prevent the previously weighed powder material from mixing into the next weighing powder material and therefore the accuracy of weighing is not satisfied. This prevents this type of system from being used in applications where a powder material must be weighed without mixing or being contaminated with other powder materials. This is often the case in paint and medicinal applications.
While automated weighing systems for powders have been developed, the success and versatility of many of these systems are in question. Weighing systems for powdery chemicals or medications are generally designed to automatically control the weighing and mixing of the powder so as to prevent the working environment from being contaminated in some instances and to avoid subjecting individuals to prolong exposure to these chemicals. One of the associated disadvantages of this type of conventional system is that the system can be inefficient in conveying powder since each single carrier, for one weighing interval, only can carry a single container to be weighed.
Another disadvantage of conventional powder transfer and weighing systems is that the powder collecting units often do not function effectively. For example, many of these systems include a powder feed pipe which disperses the powder into the container. A dust shield is provided to prevent powder from escaping into the environment, causing contamination thereof, and also to prevent undesired external dust or the like from entering the weighing system. The dust shield includes a powder collecting pipe for collecting floating powder by connecting the collecting pipe to a vacuum so that the powder is sucked through the pipe. Unfortunately, the applied vacuum causes the creation of an air stream within the system and this results in powder being carried away within the air stream to the collecting pipe rather than being dispersed into the weighing container. In addition, powder will accumulate within the collecting pipe by adhering to the internal walls thereof and, over a period of time, this powder will fall into the weighing container, thus affecting the accuracy of weighing.
Other methods for transferring and weighing small quantities of powder material have been proposed. In order to measure small quantities of powder material, instruments are often used which permit an individual to take an apportioned sample of powder material contained in a vial or the like. For example, a weighing instrument which is used to measure small quantities of powder materials is disclosed in International Application PCT/DK91/00288, which is incorporated herein by reference in its entirety. In this application, a pipette is used for taking out an apportioned sample of powder material. The pipette has a split bottom end which may be opened and closed by another suitable device, such as a tool. This instrument is designed to be disposable so that the intended quality of the product is maintained. However, these instruments are not concerned with the weighing of the powder material, but rather comprise instruments that are used to collect, transfer, and dispense the powder material to a weighing receptacle at another station, i.e., an electronic weighing station.
The present invention provides an apparatus for automatically transferring and weighing a small quantity of a powder material. The apparatus includes a weigh station including a device for weighing the powder material in a container or the like. The apparatus also includes a vacuum source and a transfer device for collecting and dispensing the powder material into the container. In one embodiment, the device is formed of a hollow body having a first end and a second end with the first end being operatively connected to the vacuum source so that a vacuum is formed in the body upon actuation of the vacuum source.
A collecting/dispensing tip is detachably coupled to the second end of the body. The tip is a hollow member with a tip orifice at one end so that a vacuum is formed in the tip upon actuation of the vacuum source and a transfer quantity of the powder material is drawn into the tip orifice. The apparatus also includes a controller for selectively actuating the vacuum source and causing movement of at least one of the transfer device and the container using a robotic device. The controller also monitors the weigh station and measurements thereat. More specifically, the powder material is collected by placing the tip orifice in close proximity to a stock supply of the powder material resulting in a transfer quantity of powder material being collected in the tip orifice when the vacuum source is actuated. The amount of powder material that is drawn into the tip orifice is referred to as the transfer quantity and is defined by several operating parameters of the apparatus. In other words, only a certain amount of powder material is drawn into the orifice tip, namely the amount of powder material which counter balances the vacuum strength. This constitutes the amount of powder material which will be transferred during operation of the apparatus of the present invention.
The powder material is transferred to the container by removing the vacuum resulting in the transfer quantity of powder material being dispensed into the container. The powder material is successively transferred to the container over a number of transfer operations until a target weight is reached. Because the container is preferably disposed on the weighing device, the weight of the container is continuously monitored until the target weight is reached. The controller preferably continuously monitors the transfer operation, including the transfer weight values for each individual transfer, so that the controller automatically determines the number of transfers necessary and also determines whether operation parameters need to be modified so as to alter the average transfer weights in order to achieve the target weight.
The apparatus of the present invention advantageously provides an automated apparatus which is capable of transferring and weighing small quantities of powder material without having the associated disadvantages of the conventional devices.
Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.